PROJECT SUMMARY/ABSTRACT Understanding the autoimmune response in human type 1 diabetes (T1D) is crucial for the design of successful immunotherapies for those at-risk for the disease as well as for those with established disease. While studies of rodent models of have greatly instructed us on the autoimmune process, the translation of successful therapies and prevention studies in the rodent models to human clinical trials has been far less successful. While we know much information concerning islet infiltrating T cells in the rodent models and islet infiltrates in humans with T1D by histology and immunohistochemistry, we previously have not had the opportunity to isolate directly the lymphocytic infiltrate from human with T1D for repertoire analysis and functional capacity. We have received islet isolations from 7 individuals with T1D and have grown or sorted directly out of the islets, 95 CD4 and CD* T cell lines. We have demonstrated the reactivity and HLA restriction of 4 CD4+ T cell lines and 3 CD8+ T cells lines (multiple reactivities are represented). The purpose of this proposal is to assay each T cell line for reactivity to whole normal islets, whole islet proteins, known islet- associated peptide targets of autoreactive T cells, to peptides derived from islet proteins that bear post- translational modifications, to define their HLA restriction, and define their effector functions. These islet- infiltrating T cells will be vital tools/reagents for investigators in the field to study the function of islet-infiltrating T cells in humanized mouse models of T1D, T cell receptor repertoire, to preserve autoreactive T cell receptors for future studies, in functional assays of autoreactive T cell interactions with T regulatory cells, B cell, antigen presenting cells and the innate immune system. Finally, these studies will inform investigators in the design of successful immunotherapies for those at-risk for T1D and especially for those with established T1D.